Air leak when stepping on brake pedal

You meant part instead of park after highlighted? A good rule is if there is a leak with the service brake applied (park brake off) the part that is leaking is bad. What is the highlighted part? I would remove that and disassemble or replace. You don't say if you tested with and without a trailer connected and if there is any difference. Why is there a disconnected/missing line (maybe the red one, vent?) next to the highlighted part?

 

So it leaks from the black line? What does that line connect to? Air leaking from a part may be air that came from somewhere else.

 

Switched what with another truck? The part that you circled in yellow?
Circled in green?
Attach the diagram that the rep sent.
Contact Bendix help, not your rep. Or the Service Engineer.
U.S. and Canada Service Engineers

 

What you circled in yellow, to the right of the green circle, where the air leaks from. Has that been replaced? You say the push fitting on that was replaced but what about the whole valve/manifold.
To verify what is leaking. Is it:
What you circled in yellow in Pic 572 or
What you circled in yellow in Pic 571

 

Is the vent line plugged by a dirt wasp? Brake chambers good and not cross feeding both emergency and service at the same time? Sometimes the basics are the causes of the big problem.

 

If it has a QR-1C valve on the park. Check it. The diaphragm inside on the compound line goes bad and leaks back into service side. The QR-1C valve itself will not show a sign of leaking on the outside or from it’s own exhaust port.

 

Someone needs to get ahold of the complete vehicle air schematic and trace backwards from the manifold port that leaks air. Something is passing air or plumbed incorrect.